Back Button does not appear in Navigationbar Xamarinforms

Question

I have a Hamburguer Menu with a Listview where in the click of the listview line I call this method to open a Modal, but the Navigationbar does not appear the Backbutton.

    public async Task OpenModalAsync(Page poPage, bool bNavigationPage = true)
    {

        if (bNavigationPage)
            await Application.Current.MainPage.Navigation.PushModalAsync(new NavigationPage(poPage), true);
        else
            await Application.Current.MainPage.Navigation.PushModalAsync(poPage, true);
    }

I have tried to use the method, but without result

    NavigationPage.SetHasBackButton(this, true);

I found that in the Pushasync method it puts the Backbutton.

Answer 1

In case in your menu harmburger you are on the "Root" screen it will not even appear.

I used in my project according to the selected item as Pushmodalasync, in this case it does not have the back button, but can use as Pushasync

You can create this way:

public interface INavigationService
    {
        Task PopModalAsync();
        Task NavigateToSubCategoria(Categoria categoria);
    }

public class NavigationService : INavigationService
    {
        public async Task PopModalAsync()
        {
            await NavigationHelper.PopModalAsync();
        }

        public async Task NavigateToSubCategoria(Categoria categoria)
        {
            await NavigationHelper.PushModalAsync(new SubCategoriasPage(categoria));
        }
    }

Codebehind :

private readonly INavigationService _navigationService;
        public CategoriasPage ()
        {
            InitializeComponent ();
            _navigationService = DependencyService.Get<INavigationService>();
        }

    void OnItemTapped(Object sender, ItemTappedEventArgs e)
            {
                var dataItem = (Categoria)(e.Item);

                _navigationService.NavigateToSubCategoria(dataItem);
            }

Xaml:

<ListView x:Name="ListaCategorias"
          ItemTapped="OnItemTapped">

    </ListView>